There has been known a technique in which a discharge electrode is arranged in an exhaust passage of an internal combustion engine, and a corona discharge is caused to occur from the discharge electrode, whereby particulate matter (hereinafter also referred to as PM) is charged and condensed or aggregated (see, for example, a first patent document). By the condensation or aggregation of the particulate matter, the number of particles in the particulate matter can be decreased. In addition, the sizes of particles in the particulate matter become large, so when a filter is arranged at a downstream side, it becomes easy to trap the particulate matter with the filter. Moreover, in a particulate matter processing apparatus using a corona discharge, there has been known a technique of ensuring insulation of a discharge electrode (see, for example, a second patent document).
However, when a corona discharge is caused to be generated, particulate matter will be crushed into fine particles by means of high-speed electrons resulting from a strong electric discharge. Then, the effect of causing particulate matter to aggregate will become low. For this reason, the particle size of the particulate matter will become small, and the number of particles in the particulate matter will increase.